Method of deacidifying gasoline



March 6, 5 J D|KEY METHOD OF DEACIDIFYING GASOLINE Filed Feb. 14, 1931 SAMUEL J. DICKEY p lNl/EN TOR ALL A T TORNEY Patented Mar. 6, 1934 UNITED STATES PATENT OFFICE 1 Claim.

The object of my invention is to provide a method of neutralizing acid-treated gasoline stocks in advance of or during a fractional distillation.

An object of my invention is to avoid the use of open steam as a distillation agent and to distil at higher temperatures than has heretofore been possible without incurring undesirable secondary results.

It is well known that the gasoline-containing fraction produced by cracking operations (the socalled pressure distillate) when treated with sulfuric acid develops certain acid bodies which are more soluble in oil than in water and cannot be removed by water washing. It is well known that when these acids are neutralized vw'th sodium hvdroxid, as is customary, the sodium salts so formed cannot be completely washed out with water.

It is also well known that when stocks containing either the acids or their salts are submitted to a distilling temperature above approximately 250 F. the oil-soluble bodies are decomposed with the formation of volatile acidic and unstable sub stances which pass over with the gasoline and greatly depreciate its quality.

The acids formed by acid-treating either pressure distillate or a gasoline fraction from crude oil are assumed to be sulfonic and/or alkyl-sulfuric acids and their sodium salts are sulfonates and alkyl sulfates. As all these bodies and perhaps other groups which may be present behave in the manner above described, I herein make use of the term sulfonates to designate all substances of whatever nature which may be present in a volatile petroleum distillate after treatment with sulfuric acid, which decompose in the above described manner on heating. I am aware that the term so used is an inaccurate and incomplete description of the mixture and variety of bodies which it designates and it is used in this sense only as a matter of convenience.

In order to avoid carrying decomposition products of the sulfonates into the gasoline vapors it is customary, at least in such refineries as pay attention to the quality of their product, to restrict the temperature to a point where decomposition does not take place, the upper limit thus fixed being about 250 F. As the end point of the gasoline is usually in the general neighborhood of 400 F., distillation at this very low temperature requires either an atmosphere consisting very largely of steam (it is not unusual to use 10 volumes of steam, liquid measure, to one volume of oil distilled) or a resort to reduced pressures approaching a vacuum.

The first alternative is costly and unsatisfactory for several reasons-costly because of excessive consumption of steam and condenser water, requiring large boiler and condenser capacityunsatisfactory because the large proportion of steam so interferes with dephlegmation that no close fractionation is possible in towers of feasible size. The second alternative involves large first cost of apparatus, high maintenance and operating charges and the same interference with fractionation, due to increased volume of vapor.

I am enabled to avoid these disadvantages, to fraetionate sharply and to work in apparatus of minimum size and cost without limitation as to temperature, in the simple manner about to be described.

The essence of my invention is to heat a flow stream of the oil to be distilled to a temperature at or above that at which the sulfonates contained therein are completely decomposed and to immediately pass the hot oil, together with any vapors which may be evolved in heating, through a body of solid caustic alkali maintained at the temperature of the oil. This contact with alka- 1i removes all the acid products of decomposition and renders the oil noncorrosive. If not already suificiently hot it may then be further heated to such temperature as will cause it to flash oil the' desired proportion of vapor. At this temperature it is passed into a combined separator and dephlegmator in which the residue and vapors are sharply fractionated.

While it is economically desirable to utilize the decomposition heat to produce or assist in producing vaporization, the treated oil may, if preferred, be cooled and stored between chemical treatment and distillation. The chemical treatment must, however, immediately follow the decomposition by heat, as at this stage the oil is highly corrosive.

In this method any water or steam accompanying the heated oil entering the alkali contactor my invention.

dissolves a proportionate amount of alkali, which may be drained as a strong solution from the bottom of the contactor and granular or flake caustic occasionally added at the top of the tower. Any excess of water in the oil causes an undue loss of caustic, and I therefore prefer to almost completely dry the oil before it enters the heating means.

In the practical application of my invention to such material as pressure distillate I proceed in the following manner, using the apparatus shown in the accompanying drawing, which will be understood to be illustrative only. In this drawing Fig. 1 is an elevation, with parts broken away, of an apparatus suited to this use, and

Fig. 2 is a diagrammatic section of a heating element which may be interposed in the apparatus of Fig. 1 at the point A.

The pressure distillate is first treated with sulfuric acid in any preferred manner and the sludge removed as completely as possible. It is not absolutely necessary to neutralize this acidtreated oil in preparation-for my treatment but it is desirable to so do in order to remove mineral acidity. This neutralization may be affected with caustic soda solution in the usual manner and the neutralized oil washed with water. This preliminary treatment is conventional and provides the raw material to which I apply the treatment of The oil so prepared should be free from mineral acids and substantially free from their salts, but will contain sulfonates and more or less finely divided entrained water.

Referring now to Fig. 1, I form the acid treated oil into a. flow stream by means of a pump not shown and introduce it through a pipe 10 into a tubularheater 11. This unit is heated by exhaust steam, hot residues or vapors or any available hot fluid, introduced and removed through pipes 12 and 13. The oil passes through the tubes and belowthe lower tube sheet a chamber is formed from which water may be withdrawn at intervals through pipe 14 and valve 15. In this unit the 0.11 may be heated to such temperature, say 200 F" -5 will cause the fine water particles to coalesce and subside.

This first heating operation is not an essential part of my invention as, first, there may not be an excess of water in the acid treated oil (the permissible maximum is say 1%) and, second, the operation may be performed in other ways. Thus, the oil may be brightened by simple settling in storage, or by filtration through clay or diatomaceous earth, or by percolation through beds of calcium chlorid or common salt. I therefore claim a preliminary drying as an optional step in my complete process but do not restrict myself to the described manner of performing it.

The dried oil leaving heater 11 passes through pipe 16 into a second heater 1'7. This may be a tubular heater as shown, supplied with any available heating fluid (steam under pressure, hot residue or vapors) through pipes 18 and 19, or it may be a fire heater such as indicated in Fig. 2. In any case it is heated in a flow stream to a temperature not below that at which the sulfonates are completely decomposed, such temperature being, in the case of pressure distillate, of the order of 270/300" F. Except from a standpoint .of operating convenience, the temperature to which the oil is heated in this step is immaterial, provided that this temperature is not below that of complete decomposition of the sulfonates. The minimum temperature for any given stock should be determined in advance and such minimum safely exceeded in operation.

Having been brought to the desired temperature the stream of hot oil passes immediately through a pipe 20 into a chamber 21 formed in the bottom of a. soda tower 22, the medial portion of which is occupied by a permeable bed of flake or granuated caustic soda or other water soluble alkali 23. Passing through this bed and being there deprived of its acid decomposition products the hot oil and any vapors which accompany it travel through a pipe 24 into a separating and fractionating apparatus 25.

Any steam or water accompanying the oil entering the soda tower will cause a part of the soda to pass into solution, and as this solution is highly concentrated and very heavy it gradually makes its way downward through the bed of caustic and settles to the bottom of chamber 21, from which it may be withdrawn at intervals through pipe 35 and valve 36. A manhole and plate 37 are provided at the top of the tower for introducing makerup alkali as required.

It is undesirable to generate a large volume of vapor in heater 17 as this so increases the bulk and velocity of the stream as to cause the soda tower to function irregularly unless an unduly large diameter be provided. This generation of vapor may be repressed by means of a valve 28 (which is preferably an automatic pressure release valve) inserted in pipe 24, by means of which the entire system up to this valve may be maintained under any desired pressure.

If the temperature attained in heater 17 is not sufficient to complete the distillation the oil 110 may be further heated by means of a heater shown in Fig. 2, inserted in the system at the point A in pipe 24. This heater consists of a pipe coil 39 communicating at each end with pipe 24, this coil being placed within a fire box 40 provided with a burner 41 and a stack 42.

Whether the heating be completed under pressure in heater 1'? or in a separate operation in coil 39, the oil is raised to a temperature at which the desired proportion will flash into vapor form as it enters the fractionating tower 25. This tower may be of any preferred construction, as for example it may be provided with bubble plates as indicated at 32. Such fractionating. towers are well known and understood and, when 125 properly proportioned and fed with vapors free from steam will give a very sharp fractionation between a top out, such as gasoline of any desired end point, and a higher boiling residue.

The residue is withdrawn from the fractionating unit 25 through pipe 33 controlled by valve 34; the vapors pass overhead through pipe 26 intoa condenser 27, cooled by water introduced through pipes 30 and 31, and the condensate is drawn to storage not shown through pipe 28.

The gasoline so produced will be found to be of exceptionally good color and stability, free from heavy ends, absolutely neutral and of improved gum-forrning characteristics.

The apparatus is immune to internal corrosion except in that small portion in which the oil has attained a decomposing temperature and has not yet been contacted with alkali. Even in this portion corrosion is much reduced by the high temperature existing at such point.

While I have referred in the preceding description to caustic soda, as a suitable alkaline reagent. it should be understood that the lwdroxids and carbonates of any of the alkali metals may be utilized, and that such reagents are comprehended 15 0 in the term water soluble alkali". The corresponding compounds of the alkali earth metals are not suitable because of their lack of solubility in water.

While I have described the contact of the hot oil with a body of solid alkali I may utilize in its stead the method described in a copending application, Serial No. 515,751, filed by Raymond C. Wheeler and Paul W. Prutzman on February 14, 1931. This application discloses the continuous contact of the hot oil with a cyclic stream of a strong solution or fusion of caustic soda within a closed vessel.

1 claim as my invention: 

